Mustang Bio (NASDAQ: MBIO) amends $4.75M at-the-market offering

Rhea-AI Filing Summary

Mustang Bio, Inc. amended its at-the-market common stock offering to allow sales of up to $4,750,000 in aggregate through H.C. Wainwright & Co. under its existing shelf registration. The company is updating the capacity it may use under General Instruction I.B.6 of Form S-3 based on its current public float. As of September 5, 2025, the public float was $20,677,132, calculated from 6,190,758 shares held by non-affiliates at a reference price of $3.34 per share. Over the prior 12-month period, Mustang Bio has offered and sold $2,102,821 of securities under this I.B.6 limitation, and future ATM sales remain subject to the one-third public float cap and the amount registered on the Form S-3.

Filed Pursuant to Rule 424(b)(5)

Registration No. 333-279891

AMENDMENT NO. 3 DATED SEPTEMBER 5, 2025

to Prospectus Supplement dated June 19, 2024

(To Prospectus dated June 12, 2024)

 

MUSTANG BIO, INC.

Up to $4,750,000

Common Stock

This Amendment No. 3 to Prospectus Supplement (this “Amendment”) further amends our prospectus supplement dated June 19, 2024 (the “Prospectus Supplement”). This Amendment should be read in conjunction with Amendment No. 1 to Prospectus Supplement (“Amendment No. 1”) and Amendment No. 2 to Prospectus Supplement (“Amendment No. 2”), the Prospectus and Registration Statement on Form S-3 containing the base prospectus and an ATM prospectus, each dated June 12, 2024 (File No. 333-279891) (collectively, the “Prospectus”), and is qualified by reference thereto, except to the extent that the information herein amends or supersedes the information contained in the Prospectus Supplement and the Prospectus, and any future amendments or supplements thereto. This Amendment is not complete without, and may only be delivered or utilized in connection with, the Prospectus Supplement, as amended, and the Prospectus, and any future amendments or supplements.

We entered into an At the Market Offering Agreement (the “sales agreement”) dated May 31, 2024, with H.C. Wainwright & Co., LLC (“Wainwright”), as Agent, relating to the offer and sale of shares of our common stock, par value $0.0001 per share, offered by the Prospectus. On June 19, 2024, we filed the Prospectus Supplement to suspend the sales agreement and to terminate the continuous offering by us under the Prospectus, effective on June 19, 2024. On July 3, 2024, we filed Amendment No. 1 to amend the Prospectus Supplement to reinstate the sales agreement and the continuous offering by us pursuant to the Prospectus and to update the amount of shares of common stock we were eligible to sell under General Instruction I.B.6 of Form S-3. On August 16, 2024, we filed Amendment No. 2 to update the amount of shares of common stock we were eligible to sell under General Instruction I.B.6 of Form S-3. We are filing this Amendment to further update the amount of shares of common stock we are eligible to sell under General Instruction I.B.6 of Form S-3.

As of September 5, 2025, the aggregate market value of our outstanding common stock held by non-affiliates, or the public float, was $20,677,132, which was calculated based on 6,190,758 shares of our outstanding common stock held by non-affiliates as of September 5, 2025, and at a price of $3.34 per share, the closing price of our common stock on July 7, 2025. In no event will we sell shares of our common stock pursuant to the Prospectus and the Prospectus Supplement, as amended by this Amendment, in an amount greater than the lower of (i) such amount as is registered on our Registration Statement on Form S-3 of which the Prospectus forms a part or, (ii) pursuant to General Instruction I.B.6, an amount with a value, taken together with the aggregate market value of all other securities sold by us or on our behalf pursuant to General Instruction I.B.6 to Form S-3 during the prior 12-month calendar period that ends on and includes the date hereof, of more than one-third of the aggregate market value of our common stock held by non-affiliates in any 12-month period, so long as the aggregate market value of our common stock held by non-affiliates is less than $75,000,000. As of the date of this Amendment, we have offered and sold $2,102,821 of securities pursuant to General Instruction I.B.6 of Form S-3 during the prior 12-month calendar period that ends on and includes the date hereof.

As a result of these limitations and the current public float of our common stock, and in accordance with the terms of the sales agreement, we may offer and sell shares of our common stock having an aggregate offering price of up to $4,750,000 from time to time through Wainwright.

Investing in our common stock involves a high degree of risk. Before making an investment decision, please read the information under the heading “Risk Factors” in the Prospectus and the documents incorporated by reference therein.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this Amendment, the Prospectus Supplement or the Prospectus are truthful or complete. Any representation to the contrary is a criminal offense.

H.C. Wainwright & Co.

The date of this Amendment No. 3 to Prospectus Supplement is September 5, 2025.

FAQ

What is Mustang Bio (MBIO) updating in this 424B5 amendment?

Mustang Bio is amending its at-the-market common stock offering to reflect the current amount it may offer and sell, allowing sales of up to $4,750,000 under its existing Form S-3 shelf.

How large is Mustang Bio (MBIO)'s at-the-market program after this amendment?

Under the amended at-the-market program, Mustang Bio may offer and sell shares of common stock with an aggregate offering price of up to $4,750,000 from time to time through H.C. Wainwright & Co.

What is Mustang Bio (MBIO)'s current public float used for the Form S-3 I.B.6 limit?

As of September 5, 2025, Mustang Bio's public float was $20,677,132, based on 6,190,758 shares of common stock held by non-affiliates at a price of $3.34 per share.

How much has Mustang Bio (MBIO) already sold under Form S-3 General Instruction I.B.6?

During the 12-month period ending on the date of the amendment, Mustang Bio has offered and sold $2,102,821 of securities pursuant to General Instruction I.B.6 of Form S-3.

What constraints limit Mustang Bio (MBIO)'s future ATM sales under this prospectus?

Future sales are limited to the lower of the amount registered on the Form S-3 and, under General Instruction I.B.6, no more than one-third of the $20,677,132 public float, together with any other I.B.6 sales in the same 12-month period while the public float remains below $75,000,000.

Who is the sales agent for Mustang Bio (MBIO)'s at-the-market offering?

H.C. Wainwright & Co., LLC acts as the sales agent under Mustang Bio's at-the-market offering agreement for sales of common stock.